The present invention relates to improved methods for preparing microcapsules and more particularly to methods in which a polyisocyanate, polyisothiocyanate or an adduct thereof is present in the internal phase wherein the improvement resides in the polyisocyanate or adduct containing an anionic moiety.
U.S. Pat. No. 4,353,809 to Hoshi et al. discloses improved methods for preparing urea-formaldehyde and melamine-formaldehyde microcapsules wherein a polyvalent isocyanate, a polyvalent isothiocyanate or an adduct thereof is added to the oily internal phase or core material. When the oily internal phase is dispersed in the aqueous phase the polyisocyanate is believed to react with water and produce a thin shell or prewall of a polyurea which stabilizes the emulsion and provides better control over the size of the microcapsules.
While the method described in the aforementioned patent has been successful, an even more effective method has now been identified.